1. Field of the Invention
Methods and apparatuses consistent with the present invention relate to wireless communication technology, and more particularly, to bandwidth-allocation in a wireless network based on a time division transmission mechanism, and transmitting and receiving data on the wireless network.
2. Description of the Related Art
As wireless communication networks become widely used, and a large-volume of multimedia data is transmitted through them, there is a need to develop a better and more efficient method of transmitting data over these networks. Due to existing characteristics of related art wireless networks, which are accessed by a large number of devices, operating characteristics of the related art wireless networks deteriorate with increased data traffic, which often results in data collision or loss during transmission. In order to prevent data collision or loss and to receive/transmit data in a reliable manner, a distributed coordination function (DCF) on a competitive basis and a point coordination function (PCF) on a non-competitive basis have been employed in wireless local area networks (LANs). In a wireless personal area network (PAN), channel time allocation has been employed.
Although these methods employed in the wireless networks reduce data collision to some degree and facilitate stable data transmission, there is still a high probability of data collision during transmission, compared to wired networks, due to various factors, such as multi-path fading and interference that affect stable data transmission. In addition, as the number of wireless devices that access a wireless network increases, data collision and loss increase.
The data collision and loss result in re-transmission of the lost data which adversely affects the throughput of a wireless network. In particular, for audio/video (A/V) data which require a high quality of service (QoS), it is a matter of great concern to have a sufficient bandwidth by reducing the number of retransmissions.
Moreover, in accordance with the growing demand for various home devices to wirelessly transmit high-quality videos, such as digital video disk (DVD) images or high definition television (HDTV) images, there is a significant demand for technical standards which can accomplish seamless communications of HDTV images.
The Institute of Electrical and Electronics Engineers (IEEE) 802.15.3c task group is developing a technological standard for transmitting a large volume of data over a wireless home network. The technological standard, which is called “millimeter wave (mmWave)”, uses an electromagnetic wave having a physical wavelength in the millimeter range (i.e., an electromagnetic wave in the frequency band of 30-300 GHz) to transmit a large volume of data. This frequency band, which is an unlicensed band, has been used by communication service providers or used for limited purposes, such as observing electromagnetic waves or preventing vehicle collision.
FIG. 1 is a diagram which compares frequency bands of the IEEE 802.11 series of standards and mmWave. Referring to FIG. 1, the IEEE 802.11b or IEEE 802.11g standard uses a carrier frequency of 2.4 GHz and has a channel bandwidth of approximately 20 MHz. In addition, the IEEE 802.11a or IEEE 802.11n standard uses a carrier frequency of 5 GHz and has a channel bandwidth of approximately 20 MHz. In contrast, mmWave uses a carrier frequency of 60 GHz and has a channel bandwidth of approximately 0.5-2.5 GHz. Therefore, mmWave has a far greater carrier frequency and channel bandwidth than the related art IEEE 802.11 series of standards.
As described above, when a high-frequency signal (a millimeter wave) having a millimeter wavelength is used, a very high transmission rate of several Gbps can be achieved. Since the size of an antenna can also be reduced to less than 1.5 mm, a single chip which includes the antenna can be implemented. Furthermore, interference between devices can be reduced due to a very high attenuation ratio of the high-frequency signal in air.
The high-frequency signal has a very short Time of Arrival (TOA) due to such a high attenuation ratio. In addition, a straight-line path signal makes it difficult to properly accomplish communications in non-line-of-sight environments. Accordingly, the former problem is overcome by employing array antennas having a high gain. The latter problem can be overcome by exploiting a beam-steering or beam-forming mechanism.
There is a diversity of transmission schemes between such a wide-band signal and a signal of a general frequency band for use in wireless LAN or wireless PAN (hereinafter, to be referred to as a narrow-band signal). Accordingly, it is necessary to adaptively modify a bandwidth-reservation process in a network where both a wide-band signal and a narrow-band signal are transmitted, unlike in the network where only a narrow-band signal is transmitted.